Manufacture of organic phosphorus compounds



cited Sta P sflfQ 3,005,003 MANUFACTURE OF ORGANIC PHOSPHORUS COMPOUNDSA'rthur Henry Ford-Moore, Salisbury, England, and 1 Geolirey -WilliamWood, Cambridge, Mass, assignors I to Minister of Supply, London,England 3 No Drawing.- Flled Mar. 31, 1955,Ser. No. 498,442; 21 Claims.(Cl. 260-461) where R and R are organic radicals. The phosphorwthiolates are corresponding isomeric compounds which containthemolecularstructureiudicated by the formula:

o a y 7 BO/ SRi It has now been found that a convenient method ofproducing organic phosphorothiolates in a state of substantial purity isto make an organic phosphorothionate and then to isomerise the latter toobtain the desired isomeric product.

The present invention consists in a process for the manufacture oforganic phosphorothiolates, which comprises first the conversion of asimple trialkyl phosphite by transesterification with a selectedaliphatic alcohol to produce a mixed trialkayl phosphite estercontaining a selected ester alkyl group (which may be a substitutedalkyl group), then the mixed tiialkyl phosphite ester produced isseparated and reacted with elemental sulphur to produce a tn'alkylphosphorothionate containing the said selected ester alkyl group andfinally the trialkyl phosphorothionate is isomerised to produce thecorresponding trialkyl phosphorothiolate.

The transesterification step is preferably carried out with the aid of acatalyst. For this purpose, when one of the starting materials is forexample triethyl phosphite, the catalyst used may be a small proportionof the corresponding acid phosphite, for example from 0.5 to 1.0 percentby weight.

The second step in the process which is the reaction of the trialkylphosphite ester with sulphur may be carried out at normal temperatureand pressure.

The third step in the process which is the isomerisation step may beetlected by heating the trialkyl phosphorothionate to an elevatedtemperature, for example, to about 130 C. for a few hours preferably inthe presence of a catalyst, for example 0.5 percent of an alkali metalalcoholate ofthe alcohol used 'inthe transesterification stepoftheprocess. f T

In order that the invention may be readily understood the process willbe described in outline by-way'of example as applied to the productionof diethyl 2 ethylthi oethylphosphorothiolate: l k

0o fl o m0 scmomsm Y, first stage in the process is the preparation of,t.he PP QPt ate mi e p p t -b a l dqt a l' t i fication of a simpletn'alkyl phosphite, namely ttiethyl phosphite with" the required alcoholcontaining 'a 'sele cted alkyl group, inthis case Z-ethylthio'etharibh'Themixture is heated at 150 C. for about two hours in the presence 7 ofa small quantity or diethyl hydrogen phosphite, for

. instance from 0.5 to 1.0 percent'by weight, which acts'as catalyst.-The product is a mixture of ethanol audjdiethyl Q-ethylthioethylphosphite j The reaction'which occurs is represented by the following"equation":

Et0H+ (EtO RoCH 'CH SEt The ethanol is removed by distillation and theresidual mixedtrialkyl phosphite ester is reacted with powdered sulphurat ordinary room'temperature and atmospheric pressure in a flask fittedwith a condenser. This additive reaction which isthe second stage of theprocess is rep resented as follows: V a s (EtOhPHO CH:OHgSEt+S=(EtO)1Pomrrrsnr The product of' this reaction is'die'thyl 2-ethylthioethylphosphorothionate.

The phosphorothionates possess a tendency to isomerize tophosphorothiolates. In accordance with one feature of the presentinvention this tendency is accelerated with the aid of a catalyst. Thusin the third stage of the present process the diethyl Z-ethylthioethylphosphorothionate is heated to a temperature of about 130 C. for a fewhours, say five hours in the presence of about 0.5 percent by weight ofthe sodium derivative of the alcohol used in the first stage of theprocess, that is to say sodium 2-ethylthiothano1ate, NaOCH CH SEt, whichacts as a catalyst. During this heating the phosphorothionate isisomerised almost completely to the corresponding phosphorothiolate, thecomposition of which is indicated by the following formula:

Under favourable conditions the yield may be percent of the requiredphosphorothiolate, based on the phosphite ester (EtO) P.0CH CH,SEt.

The process according to the invention is illustrated by the followingspecific example which comprises three steps, namely,

(1) The catalyzed transesterification of triethyl phosphite to producethe mixed phosphite, diethyl Z-ethylthioethyl phosphite.

(2') additions of elemen'tal sulphur to produce the requiredphosperothtonate, and

{3) The catalytic isomerization of the phosphorothionate to thephosphorothiolate.

EXAMPLES (1) Diethyl Z-ethylthioethyl phosphite Triethyl phosphite (41.5g.: 0.25 mole), ethylthioethanol (26.5 g.; 0.25 mole), and diethylhydrogen phosphite (0.3 cc.) were heated in a flask with a short columnattached to a downward condenser, to 145150 C., in antoilbath in: aslowstream of nitrogen, "lhe distillation of ethanol (10 cc.) seemedcomplete in one hour-, but the: reactionmixturewas heated fora furtherhour. a fractionation under reduced pressure, two low boilingfractionsyc onsistingmainly of triethyl phosphite and ofethylthioethanol were obtained followed; by the product B.P. 85-87C./0.7 mm. and a residue. The product was redistilled and had a B.P. 85C./0.6 mm. yield 56.5% based on the thioalcohol used.

(2) Diethyl Z ethyI IhiOethyI phosphorothionqte Diethyl2etliylthioethylphosphite (045.5 g'.) was treated sulphur flowers (6.4g)added over'abbut' one-half hour. Y He'at was. developed and'mest ofthe:murmur-went into solution. After standing tor one hour at O. C.,thematerial was filtered from a Iittle'urireacted sulphur. The yieldfwaspractically theoretical; The product boiled at 85 8'6. C./0.00'2 mii.jbuti the ref ractiire index of the higher fractions. (B.P. 86487:"C./0.0005' mm.) indicated that some isomerisation'had taken place'I'he-infra-red absorption spectrum of-the. undistilledflmaterialshowedit to be free from phosphorotliiolate isomer. 7 V 7 i V i -(-3);0,0-diethyl S-Z-ethylthibkihfl phosphorothiolat 7 presence. 0t adiscrete methyl radical in. the substituted &S0ns-(l950),-pages'196,235.

alkyl group, that is to say, in the 2-methylthioethyl group appearstoinhibit the isomerisation;

Accordingly, the following claims are to be construed so as to excludethe phosphorothionates which contain 5 a discrete methyl substituent ashereinbefore specified.

. The invention is not restricted to the production of neutral aliphaticesters of phosphorothiolic acids in which one ester group is substitutedby an aliphatic-mercapto group as hereinbefore described, but theprocess of the invention may also be used for the production of othersuch phosphorothiolates in which one ester group contains a substituentorganic radic'a'l other than an aliphaticmercapto group.

Weclaim:

1. Process for producing, a'low'er elk-yr phosphor c thiclatewhichcomprises-transesterifying'a lowertrialkyl. phosphite with an;alkyl thioalkanoli having, lower alkyle groups in the presence of a;dialkyl'hydrogen phosphiteca'talyst at temperature ofabout l to I 0.;-the resulting lower trialkyl' phosphite ester with elemental V sulfur toproduce the lower trialkyl. phosphorothionate,

isorheri'zing, the latter in the presence'of alkalijrfietalalcoholateat' about C. to forr' njthe-lowerftriullryiphosphorothiola'te.

25 2. Process for producing jgis hyisz-stfiynfitoemyr References Citedin the file of this patent UNITED STATES PATENTS Gzeinjski ....Aug". 7Merrill-i June 17 1952 r ....;i. aaiJ-a-Q-x-Q; OTHER REFERENCES Fukutoet al.: J. Am. Chem. Soc.," 76, 5103 (1954) (Oct. 20, 1954). Kosolapotf;Qrganokhosphorus-Compounds," WileyDiethyl2rethylthioethylphosphorothionate (15 'g.; 1.1 7

1. PROCESS FOR PRODUCING A LOWER ALKYL PHOSPHOROTHIOLATE WHICH COMPRISESTRANSESTERIFYING A LOWER TRIALKYL PHOSPHITE WITH AN ALKYL THIOALKANOLHAVING LOWER ALKYKL GROUPS IN THE PRESENCE OF A DIALKYL HYDROGENPHOSPHITE CATALYST AT A TEMPERATURE OF ABOUT 145 TO 150*C., REACTING THERESULTING LOWER TRIALKYL PHOSPHITE ESTER WITH ELEMENTAL SULFUR TOPRODUCE THE LOWER TRIALKYL PHOSPHOROTHIONATE, ISOMERIZING THE LATTER INTHE PRESENCE OF AN ALKALI METAL ALCOHOLATE AT ABOUT 130*C. TO FORM THELOWER TRIALKYL PHOSPHOROTHIOLATE.